Intra prediction exploits spatial correlation within a picture or within a picture region. In order to improve coding efficiency, the High-Efficiency Video Coding (HEVC) standard exploits block-based spatial prediction extensively. In HEVC, multiple Intra prediction modes are used to exploit spatial features. The size of the Prediction Unit (PU) for Intra coding can be 32×32, 16×16, 8×8, or 4×4. The number of Intra prediction modes is 35, which includes 33 directional prediction modes, one DC mode and one planar mode.
Intra prediction in video coding standards such as AVC and HEVC consist of predicting the samples in the current block from already reconstructed left and top neighboring samples, referred to as reference samples. HEVC intra prediction uses angular prediction with thirty-three angles to predict the samples in the current block along the direction of one of the thirty-three angles. In addition depending on the block size and the angle of the prediction, the reference samples are smoothed using a [1 2 1]/4 filter to provide a smoothly varying prediction signal.